1. Field of the Invention
The present invention relates to cameras which recognize the reloading of partially used film cassettes.
2. Description of the Prior Art
A photographer sometimes desires to remove a film cassette from his camera before all of the film frames have been exposed. This is likely when using 35mm cameras because the cassettes for these cameras frequently contain sufficient film for as many as 36 full frame exposures. To illustrate, let us assume a situation where a photographer loads a camera with a film cassette containing a 36 exposure color film having an ASA number of 400 and "takes" twenty pictures, i.e. sequentially exposes 20 consecutive film frames to form latent images. He then decides to take pictures of another subject for which a 20 exposure, black and white, general purpose film having an ASA number of 125 is more suitable. The photographer carefully rewinds the color film back into its cassette, leaving a part of the filmstrip leader tongue extending from the cassette, removes the cassette from the camera, and loads the camera with a new cassette containing the black and white film. If the photographer plans to use the 16 unexposed frames of the removed color film, at some later time, he will probably note somewhere on the removed cassette the number of the last film frame that was exposed. Sometime later, when the partially used cassette of color film is reloaded into the camera, the photographer advances the film to locate the first unexposed film frame for exposure. Of course, if the photographer forgot to annotate the cassette, or misinterprets his notes or fails to properly locate the film in the camera, he may advance the film too far, wasting one or more film frames. On the other hand, if the filmstrip is insufficiently advanced, double exposure results. In an even worse case, if the photographer ignores his notes or forgets to advance the film beyond the first frame, there will be double exposure of the first twenty film frames.